This invention relates to novel photographic processes, elements and physical developer solutions. In a particular aspect, it relates to the use of photosensitive compounds of metals from Groups VIIIB and/or IB of the periodic table in processes for the formation of formazan dye images.
A large number of photographic processes are known, ranging from conventional silver halide systems to various non-conventional processes such as diazo processes, photopolymerization and various direct printout or photochromic materials. An ideal photographic system requires only a small amount of exposure from the particular radiation source being used to record the desired information. Thus, high speed photographic systems are generally characterized by the incorporation of a catalytic amplification step. In conventional silver halide systems, this amplification step is the chemical reduction of silver halide catalyzed by the Ag(O) latent image.
It is known in the art to produce formazan dye images by the reduction of the corresponding tetrazolium salt. For example, U.S. Pat. No. 3,152,903 to Shepard describes a process wherein a light activated reducing agent (photoreductant) reduces a tetrazolium salt to a formazan dye. The two electron photoreductant system described in U.S. Pat. No. 3,152,903 requires that two photons of energy be absorbed by the light activatable reducing agent to form one molecule of formazan dye. The unit quantum type process described by Shepard is inherently slow requiring long exposure times.
The use of tetrazolium salts to replace silve metal in a fixing bath is described in U.S. Pat. Nos. 3,642,478; 3,655,382; and 3,671,244.
It is known that various compounds of metals from Group VIIIB and/or IB of the periodic table can be used to form latent image centers for the catalytic deposition of heavy metals from metal physical developer solutions. Processes of this type using palladium complexes are described in Yudelson and Gysling U.S. Pat. No. 3,719,490, Yudelson and Dernbach U.S. Pat. No. 3,598,587 and Yudelson and Dernbach U.S. Pat. No. 3,650,748. Processes of this type using copper complexes are described in copending applications Ser. No. 365,375 filed May 30, 1973, Ser. No. 365,374 filed May 30, 1973, and Ser. No. 409,828 filed Oct. 26, 1973.
The processes of preparing visible metal images from photogenerated metal nuclei described above have several disadvantages. These include (1) complex chemical formulations are required including such components as metal salt, reducing agent, complexing agent, pH buffers, stabilizers and brighteners; (2) such baths are often not stable for extended periods of time; (3) baths may require elevated temperatures to be useful; and (4) color images can not be obtained.